1. Field of the Invention
The present invention relates to a process for production of a flame-resistant and smoke-retardant polyurethane foams.
2. Description of the Prior Art
It is well known to produce polyurethane foams by using polyhydroxyl compound, polyisocyanate, water and/or other foaming agents a catalysts, a foam stabilizer and the like.
Various foams such as flexible, semi-rigid and rigid polyurethane foams have been produced depending upon number of functional groups, molecular weight, main chain structure and the like, of the polyhydroxyl compound and the polyisocyanate.
These foams are broadly used as a seat or cushion for furniture, cars, airplanes and ships, material for clothes and building and the like.
A flame-resistant polyurethane foam is required for the above applications, and various methods imparting flame-resistance to the polyurethane have been researched. However, known methods that is, methods using a flame-resistant agent of the addition type or reaction type such as phosphorus compounds, combination of halogen and phosphorus compounds, and a metal oxide such as antimony oxide and the like can impart flame-resistance to some extent, but the polyurethane foam thus obtained generates much smoke upon burning. The polyurethane foam containing a ring structure such as an isocyanurate ring structure or an imide ring structure is not easily decomposed by heat due to its heat resistant ring structure. Therefore, using such ring structure is one of the effective methods for imparting flame-resistance, but said foam is apt to become rigid polyurethane foam generates much smoke in burning. Accordingly, said polyurethane foam can not be simultaneously flame-resistant and smoke-retardant.
In view of the use of polyurethane foams, it is strongly desired to use polyurethane foams having flame-resistance, smoke-retardation and low poisonous character, particularly for cars, buildings and furniture.
Heretofore, as a catalyst for preparation of polyurethane foam, an organic tin compound or a tertiary amine compound has been usually used, but an alkaline earth metal compound has not been used at all. For example, J. W. Britain and P. G. Gemeinhardt: Journal of Applied Polymer Science, 4, 207-211(1960) discloses that an alkaline earth metal compound such as a compound of barium, magnesium, calcium or strontium is hardly effective as a catalyst. Accordingly, the catalytic behavior of alkaline earth metal compounds has not been investigated.
There are the following two kinds of the catalytic activities for polyurethane foaming reactions. One is a catalytic activity for chain extension and gelation reaction including formation of a urethane bond or urea bond by reacting a polyisocyanate compound with a polyhydroxyl compound having a active hydrogen or water, and formation of an allophanate bond or buiret bond by reacting the above mentioned urethane or urea bond with a polyisocyanate compound. The other is a catalytic activity for foaming reaction accompanied by generating carbon dioxide gas by reacting the polyisocyanate compound with water. The term "catalytic activity" for urethane foaming reactions refers to the effectiveness for both of the above-mentioned reactions.
Many conventional catalysts for polyurethane foaming are effective usually in only one of the gelation reaction and the foaming reaction and therefore, several catalysts are used in combination rather than alone.